This invention relates to a process for validating permeation measurements made through closed containers; more particularly, the process is useful in validating permeation measurements through materials forming closed containers, where the containers have one or more closure members which may contribute to leakage and may therefore be a source of error in the permeation measurements.
The permeation of organic and other vapors through the walls of a closed container can be measured according to techniques which are well known in the prior art. For example, the closed container can be filled or partially filled with the liquid whose vapor permeation is of interest, and the container can be placed within a chamber through which an inert carrier gas such as nitrogen is permitted to flow. The inert carrier gas will pick up vapor molecules which have permeated through the walls of the container as the carrier gas flows through the chamber, and the carrier gas is subsequently passed through a vapor detector where a measurement may be made of the vapor gas concentration contained in the carrier gas. This measurement can be normalized to provide a calculation of the amount of vapor permeating through the container walls per square meter per day, to provide a basis for comparing the relative permeation through a number of different materials which undergo the same tests, and therefore to provide a basis for selecting materials which permit the least permeation in actual practice.
Since the permeation measurements described above frequently involve very small measured quantities, frequently in the range of parts per billion, it becomes extremely important to prevent any spurious leakage anywhere in the testing apparatus or, to be able to quantify any leakage that may exist in the testing apparatus or in the materials being tested. When the closed container undergoing testing contains closures of one type or another, the leakage through the closures becomes a significant factor which must be accounted for. Even a tiny amount of leakage through a supposed xe2x80x9csealedxe2x80x9d closure can distort the measurements sufficiently to render the test results unreliable or meaningless, and therefore a closure xe2x80x9csealxe2x80x9d on a container demands particular attention, either to ensure that the closure is completely sealed or to account for the amount of vapor leakage through the closure. However, when permeation measurements involve vapor permeation in the parts per billion range, it is virtually impossible to know for certain whether the container closure is contributing to or distorting the measurements. It is therefore very important to be able to account for any leakage which may exist through closures, and the present invention provides a process for accounting for such leakage, and thereby validating the permeation measurements made through any of the well known techniques which are used in practice.
The invention is particularly adaptable for validating permeation measurements made through tubular materials such as hoses or other liquid flow lines, but it can also be used for evaluating heat seals on plastic containers or closure members on a variety of containers.
A process for validating permeation measurements through closed containers containing one or more closure members, comprising the steps of making a first permeation measurement through a container of a predetermined first size with the closure member(s) in place, and next making a second permeation measurement through a container of the same material and thickness, of a predetermined second size with the closure member(s) in place, and then calculating the theoretical permeation difference or ratio of the two sizes of material and subtracting an equal permeation measurement contribution from the first and second permeation measurements until the actual permeation difference or ratio of the two permeation measurements is in the same relative relationship as the theoretical difference or ratio.